<h1 id="tennessee-congressional-districts">2020 Tennessee Congressional
Districts</h1>
<h2 id="redistricting-requirements">Redistricting requirements</h2>
<p>In Tennessee, there are no rules for redistricting Congressional
districts (<a
href="https://www.ncsl.org/research/redistricting/redistricting-criteria.aspx">NCSL</a>).</p>
<h3 id="algorithmic-constraints">Algorithmic Constraints</h3>
<p>Although there are no rules, in practice, the state does avoid
splitting its boundaries. The 2010 map split 8 of its 95 counties, and
split only 4 of the 228 municipalities in our data, and only 2 of the 20
largest municipalities. That said, the 2020 map split the city of
Nashville, splitting its county into three congressional districts,
showing that these practices are not set in stone.</p>
<p>Therefore, to enforce some county splitting avoidance, we took 20
largest cities in Tennessee (each with a population of at least 40,000)
and concatenated them with counties so that these “pseudo-counties” were
smaller units of geography that delineated major cities as well as
counties. We then allowed the simulation to split at most 8 of these
pseudo-counties.</p>
<p>We enforce a maximum population deviation of 0.5 percent.</p>
<h2 id="data-sources">Data Sources</h2>
<p>Data for Tennessee comes from the ALARM Project’s <a
href="https://alarm-redist.github.io/posts/2021-08-10-census-2020/">2020
Redistricting Data Files</a>. The 2022 boundary comes from the <a
href="https://thearp.org">American Redistricting Project</a>.</p>
<h2 id="pre-processing-notes">Pre-processing Notes</h2>
<p>See pseudo-county definition above.</p>
<h2 id="simulation-notes">Simulation Notes</h2>
<p>We sample 5,000 districting plans for Tennessee across two
independent runs of the SMC algorithm. Pseudo-counties created as above
and used as a hard SMC constraint. No special techniques were needed to
produce the sample.</p>
<h2 id="contents">Contents</h2>
<ul>
<li><code>TN_cd_2020_stats.csv</code> contains summary statistics on the
sampled redistricting plans</li>
<li><code>TN_cd_2020_plans.rds</code> is a compressed
<code>redist_plans</code> object, which contains the matrix of
precinct/block assignments and may be used for further analysis.</li>
<li><code>TN_cd_2020_map.rds</code> is a compressed
<code>redist_map</code> object, which contains the precinct/block
shapefile and demographic data.</li>
</ul>
<p>Both the <code>redist_plans</code> and <code>redist_map</code> object
are intended to be used with the <a
href="https://alarm-redist.github.io/redist/">redist package</a>.</p>
<h3 id="codebook-for-summary-statistics">Codebook for summary
statistics</h3>
<ul>
<li><code>draw</code>: unique identifier for each sample. Non-numeric
draw names are real-world plans, e.g., <code>cd_2010</code> for an
enacted 2010 plan.</li>
<li><code>district</code>: a district identifier. District numbers
roughly match those in the enacted plan, but the correspondence is not
perfect.</li>
<li><code>chain</code>: a number identifying the run of the
redistricting algorithm used to produce this draw. Used for diagnostic
purposes.</li>
<li><code>pop_overlap</code>: a number indicating the fraction of people
in this plan who reside in the same-numbered district in the enacted
plan.</li>
<li><code>total_pop</code>: the total population of each district.</li>
<li><code>total_vap</code>: the total voting-aged population of each
district.</li>
<li><code>pop_*</code>, <code>vap_*</code>: total (voting-aged)
population within racial and ethnic groups for each district. Variable
codes documented <a
href="https://github.com/alarm-redist/census-2020#data-format">here</a>.</li>
<li><code>plan_dev</code>: the maximum population deviation among
districts in the plan. Computed as
<code>max(abs(distr_pop - target_pop)/target_pop)</code>.</li>
<li><code>comp_edge</code>: compactness, as measured by the fraction of
internal edges kept. Higher values indicate more compactness.</li>
<li><code>comp_polsby</code>: compactness, as measured by the
Polsby-Popper score. Higher values indicate more compactness.</li>
<li><code>county_splits</code>: the number of counties which belong to
more than one district.</li>
<li><code>muni_splits</code>: the number of Census Designated Places
which belong to more than one district.</li>
<li><code>*_##_dem_*</code>, <code>*_##_rep_*</code>: vote counts for
statewide Democratic and Republican candidates in a certain election.
More information <a
href="https://github.com/alarm-redist/census-2020#data-format">here</a>.</li>
<li><code>adv_##</code>, <code>arv_##</code>: average vote counts for
statewide Democratic and Republican candidates in a certain year. More
information <a
href="https://github.com/alarm-redist/census-2020#data-format">here</a>.</li>
<li><code>ndv</code>, <code>nrv</code>: averages of the
<code>adv_##</code> and <code>arv_##</code> variables across all
available elections.</li>
<li><code>ndshare</code>: normal Democratic share, computed as
<code>ndv / (ndv + nrv)</code></li>
<li><code>e_dvs</code>: average Democratic vote share, computed as the
average of the Democratic vote share when first scored under each
statewide election.</li>
<li><code>pr_dem</code>: probability seat is represented by a Democrat;
calculated as the fraction of statewide elections under which the
district had a majority Democratic share.</li>
<li><code>e_dem</code>: expected number of Democratic seats for the
plan; equivalent to summing the <code>pr_dem</code> values across
districts</li>
<li><code>pbias</code>: partisan bias at 50% vote share, averaged across
all available elections. Positive values indicate Republican bias.</li>
<li><code>egap</code>: the efficiency gap, averaged across all available
elections. Positive values indicate Republican bias.</li>
</ul>
